Tuesday, October 19, 2010

Fossilised iceblocks shed light on early life

The discovery of blocks of nettle which sank to the bottom of the sea trapped in ancient icebergs has sparked a new understanding of a bizarre group of creatures. The research published today in the Australian Journal of Earth Sciences, has also forced a rethink of the situation that existed more than 500 million years ago.

Associate Professor Victor Gostin and colleagues at the University of Adelaide found evidence of ancient icebergs mixed in with volcanic rocks which were spewed out when an asteroid hit the earth between 635-542 million years ago. The 4.7-kilometre asteroid left a 90-kilometre crater in what is now Lake Acraman in the Gawler Ranges of South Australia.

Icebergs carry coarse debris, boulders and grains. As the iceberg melts it is dragged to the bottom by the weight of the debris, then the ice melts and the surrounding mud eventually buries the debris, creating this sort of fossilised iceblock.

The Australian Geologist, Professor Malcolm Walter of the University of New South Wales says the research resolves matters around the timing and record of the glaciations, the impact and the rise of the Ediacaran biota. He explained the effect of the icy climate and asteroid impact as a "double whammy" that paradoxically led to the "flourishing of exotic plankton and the first macroscopic animals".

The Ediacaran fauna, which were the first large complex life forms to emerge. They resembled jellyfish, sponges, marine worms, plus other organisms whose body plan resembles nothing alive today.

Gostin is eager to explore other glacial deposits that formed around the same time in other parts of the world to see if there is further evidence of the asteroid's impact on the microscopic creatures at that time.